Conventionally, masks of various kinds such as antibacterial masks, antiviral masks, antiallergic masks, and deodorizing masks have been disclosed. Among them are a particularly large number of deodorizing masks containing deodorizers: for example, a mask with an activated carbon sheet in its filter (see Patent Literature 1), a mask with an odor adsorption sheet made of a water-containing magnesium silicate clay mineral (see Patent Literature 2), and a deodorizing mask with an air-permeable material attached to its air-permeable portion wherein at least a metal selected from Fe, Mn, Al, Zn and Cu, and a reaction product of the metal and oxypolybasic acids coexist in the air-permeable material (see Patent Literature 3). However, adequate deodorizing effects are not expected from physisorption-type deodorizers, such as activated carbons. Besides, prolonged use of these deodorizers causes release of adsorbed malodorous gases. The water-containing magnesium silicate clay minerals, whose original deodorizing effects are not so high, cannot obtain satisfactory deodorizing effects unless these materials are abundantly used and sheet treatments are properly performed. As to the materials coexistently containing reaction products of the metals and the oxypolybasic acids but with no binder contained therein, it is difficult to use large quantities of these materials in the air-permeable portion. This may cause maldistribution of the deodorizer, diminishing its deodorizing effect. As is the case with the before-mentioned materials, an adequate deodorizing performance is not possible.
So far has been disclosed a three-dimensional deodorizing mask with a four-layer structure, wherein malodorous gases can be thoroughly absorbed by a nonwoven fabric with porous ceramic particles adhered thereto (see Patent Literature 4). More specifically describing the mask, porous ceramic particles are spread and adhered onto a polyester-based nonwoven fabric by means of an acrylic resin so that an ⅓ area of the ceramic particles is thereby covered, and a microfiber nonwoven fabric is further provided on the face side of the deodorizing nonwoven fabric as a collection layer. Any details of the deodorizing performance of this particular invention are unknown because types of used gases and duration of its deodorizing effect are not stated. This conventional example did not study the deodorizing effect of the whole mask but only confirmed the deodorizing ratio in the deodorizing test where the deodorizing nonwoven fabric alone was solely used, which was 96% by volume. This deodorizing ratio is extremely low for practical use. As is known from the Weber-Fechner's law, the human sense of odor is commonly poor. For example, reduction of a malodorous gas by 90% by volume can only be perceived as not more than 50% reduction. Therefore, one is never satisfied with the deodorizing effect unless the deodorizing ratio is, at the minimum, 99.9% or more by volume, or desirably, 99.99% or more by volume.
A deodorizing mask is proposed which includes, in its layers, a fabric, paper or chemical product having ion exchangeability targeted for ammonia-containing gases (see Patent Literature 5). With such a deodorizer characterized by ion exchangeability, which is a chemisorption-type deodorizer, a high deodorizing performance may be possible. This document, however, discloses neither specific components nor formulation of the deodorizer, failing to demonstrate whether the deodorizing effect of this mask meets the requirements of practicality or whether the production of such a mask is feasible.
Another example which has been disclosed is a three-dimensional mask formed in the shape of a bowl wherein a nonwoven fabric forming a mask body includes, by 30% to 50% by mass, a fiber carrying a metal complex having a redox ability and/or a fiber carrying metal ions (see Patent Literature 6). Such a deodorizer should be included in the category of chemisorption-type deodorizers, which may accomplish a high deodorizing performance depending on a method of use. Yet, the mask, if formed in a monolayer structure, often retains therein malodorous gases passing through. Again, the deodorizing effect of this mask is not very high.
In the meantime, chemisorption-type deodorizers have been developed, which are advantageous in that small quantities enable high deodorizing performances (see Patent Literatures 7, 8, and 9). Such chemisorption-type deodorizers capture odors through reactions, thereby effectively eliminating odors in short periods of time. However, offensive odors to be captured by masks are generated by gaseous matters, and contacts between the deodorizers and malodorous gases are instantaneous. As far as a nonwoven fabric carrying a deodorizer has an air permeability, there are certainly some malodorous gases passing through the nonwoven fabric without contacting the deodorizer. Thus far, deodorizing masks, which advantageously reduce any offensive odors to a hardly-perceivable level, are yet to be invented. On the other hand, consumers are increasingly demanding comfortableness when they are wearing the masks. They want a mask that causes no discomfort and accomplishes a high deodorizing performance by efficiently adsorbing malodorous gases.